1. Field of the Invention
The present invention relates to a printed circuit board and a method of production of an electronic apparatus.
2. Description of the Related Art
In the past, integrated circuits, resistors, capacitors, and numerous other electronic devices have been surface mounted on printed circuit boards by reflow soldering.
Normally, for surface mounting an electronic device on a printed circuit board by reflow soldering, first a printing plate for printing solder paste is arranged over the board electrodes of the printed circuit board and cream-like solder paste is coated on the printing plate to coat the board electrodes with solder paste. Next, the printing plate is removed, the electronic device is placed on the printed circuit board, and solder melted by hot air heating or infrared heating called “reflow” is used to bond the electronic device electrodes and the board electrodes.
A printed circuit board carrying an electronic device produced by reflow soldering in this way is inspected by an inspection for the appearance or an electrical test connecting the board electrodes and device electrodes and then used to produce an electronic apparatus. However, if the solder melted by the reflow does not stop at between the electronic device electrodes and the board electrodes and leaks outside of the electronic device, sometimes the warping of the electronic device and the printed circuit board at the time of reflow will result in soldering failure etc. and the problem of a drop in yield of the electronic apparatuses.
Using FIGS. 1A to 1C, an example of soldering the board electrodes provided on a printed circuit board and device bottom electrodes provided at an electronic device will be explained. FIG. 1A is a side view showing a device electrode arranged at the bottom of an electronic device 20a, that is, a device bottom electrode 22a, a board electrode 12a of the printed circuit board 10a, and a solder joint 24a, FIG. 1B is a top view showing the positional relationship between the device bottom electrode 22a and the board electrode 12a, and FIG. 1C shows a mode of mounting an electronic device 20b on the printed circuit board 10b. 
As shown in FIG. 1A, at the solder joint 24a between the electronic device electrode 22a and board electrode 12a, the solder melted at the time of the reflow did not stop between the electrodes and leaked to the outside of the electronic device. There was less solder between the electrodes and a low level of height of solder between the electrodes.
As shown in FIG. 1A, if the amount of solder between the electrodes is small, as shown in FIG. 1C, when warping of the electronic device 20b and printed circuit board 10b occurs due to the thermal stress at the time of reflow, unless the molten solder is high enough to allow for that deformation, the device bottom electrode 22b and board electrode 12b will end failing to bond.
Japanese Laid-open Patent Publication No. 2005-228959 proposes a method of using electrodes at the side surface of a device and firmly bonding with the electrodes at the side surfaces of the device so as to avoid the phenomenon of such bonding failure between electrodes at the time of reflow.
The method proposed requires that electrodes of an electronic device be made device side electrodes. However, along with the higher density of electronic apparatuses, electronic devices are being made smaller in size. It is therefore difficult to form side electrodes at the outer edges of an electronic device. Further, device side electrodes are arranged to cover the outer edges of the electronic device. The board electrodes are extended in the direction of the outer edges of the electronic device and the area occupied by the electronic device on the printed circuit board is increased, so there is the problem that this impairs the increased density of electronic apparatuses.